In recent years, a transfer system that performs wireless power transfer (also called contact-free or contactless power transfer) on CE devices (Consumer Electronics devices) such as mobile phones and portable music players has attracted attention. In such a transfer system, for example, an electronic apparatus (such as a mobile phone) having a power receiving unit may be charged by placing the electronic apparatus on a power transfer unit such as a power transfer tray. In other words, in such a transfer system, the power transfer is allowed to be performed without interconnecting the power transfer unit and the power receiving unit by a cable or the like.
Examples of methods of performing such wireless power transfer may include an electromagnetic induction method and a magnetic field resonance method (also called magnetic resonance method) using resonance phenomena. In these methods, power is transmitted with use of magnetic coupling between a coil of a power transfer unit and a power receiving coil of a power receiving unit. Among them, as compared with the electromagnetic induction method, advantageously, the magnetic field resonance method is allowed to transmit power even if the power transfer unit and the power receiving unit are away from each other, and transfer efficiency in the magnetic field resonance method does not particularly drop even if positioning between the power transfer unit and the power receiving unit is insufficient.